What is the risk to buying stocks during a crash?

As a layperson, the idea of buying up stocks during a crash when stock prices drop makes sense, as those prices seem very likely to go back up after the crash, barring economic catastrophe.

The idea feels obvious to me, with the basic buy low, sell high mentality. Surely, a myriad of others have had the same idea. Does this actually work, or are there things this doesn't account for that would sink the whole effort?